A high-temperature diffraction study of the solid solution CaTiOSiO4-CaTiOGeO4

作者：Ellemann Olesen R^*; Malcherek T

来源：American Mineralogist, 2005, 90(8-9): 1325-1334.

DOI：10.2138/am.2005.1729

The structure of CaTiOGeO4 (CTGO) has been refined using single crystal X-ray diffraction data. CTGO is isostructural with titanite, CaTiOSiO4. The displacive P2(1)/a-A2/a phase transition analogous to titanite has been studied by in situ heating X-ray powder diffraction and transmission electron microscopy. The transition is accompanied by the disappearance of superstructure reflections, k + l = 2n + 1, which are replaced by diffuse scattering for T > T-c. The diffuse scattering is seen as streaks along b* in high-temperature TEM SAD. Lattice parameters as a function of temperature and composition were determined by X-ray powder diffraction between room temperature and a maximum of 1123 K. Strain analysis of CTGO indicates a transition temperature of T-c = 588 +/- 4 K and the additional occurrence of an isosymmetric anomaly at T-i = 800 +/- 25 K. There is complete solid-solution along the join CaTiO(GexSi1-x)O-4. The lattice parameters across the solid solution vary continuously and the structural phase transitions were identified based on the determination of spontaneous strain associated with the transitions. The e(11) and e(13) components dominate the strain tensor. All compositions across the solid solution exhibit close to tricritical behavior and nearly constant scalar strain.

• 出版日期2005-9